Re: [Discuss-gnuradio] On Off Keying

From:

Brian Padalino

Subject:

Re: [Discuss-gnuradio] On Off Keying

Date:

Mon, 29 Sep 2008 17:28:21 -0400

On Mon, Sep 29, 2008 at 4:40 PM, Johnathan Corgan
<address@hidden> wrote:
> On Mon, Sep 29, 2008 at 11:52 AM, sri ram <address@hidden> wrote:
>
>> 3. However, for a tx. stream of 1's and 0's mixed, I still see the received
>> amplitude (real part) showing the beat frequency continuously and not going
>> to 0 for the 0 bits.
>
> When you send alternating 1's and 0's, you are creating a baseband
> square wave of constant power. The DC offset is half your baseband
> transmit amplitude, and that energy at DC is upconverted to your
> carrier frequency. On receive, since you have a frequency offset, you
> will see a continuous beat frequency resulting from this constant
> carrier. Superimposed on this will be the harmonics of your square
> wave up to the Nyquist limit of your baseband sampling rate, or up to
> the cutoff frequency of the RRC filter if it is in use.
Don't some of the daughterboards also have some AGC built in? I can
see if the interpolation rate is not high enough, the signal power
will not go down enough (especially after the RRC filtering) to really
look like much of a difference if any due to the AGC circuitry and
other transients that may occur on signals quickly coming on then off.
Please correct me if I am wrong, but I think using a very large
interpolation rate might help clarify the situation.
Brian